1. Field of the Invention
The present invention relates to devices useful for cutting a material. More particularly, the present invention relates to devices such as cutting insert assemblies useful for cutting a material such as metal.
2. Description of the Invention's Background
Cutting inserts are useful for cutting materials such as metals. For such a purpose, a cutting insert is commonly mounted to a cutting tool, and the cutting tool is rotated while the material is fed toward the cutting tool or the cutting tool is fed toward the material. A cutting edge of the cutting insert cuts off a small piece of the material, i.e., a chip, each time it passes across the material with rotation of the cutting tool. The problem with such an arrangement, however, is that the area of the cutting edge in contact with the work quickly becomes very hot due to the friction generated by cutting, which causes relatively rapid degeneration of the cutting edge and thus causes the cutting insert to have a relatively short useful life. Shorter useful lives in cutting tools requires the cutting process to be interrupted, the machine stopped and the cutting tool removed and replaced prior to resuming cutting.
To lengthen the useful life of a cutting insert, cutting inserts have been designed with multiple or continuous edges, such that the cutting insert may be indexed to present a new edge or a new portion of an edge once one edge or portion thereof has worn out. For example, U.S. Pat. No. 4,812,087 to Stashko discloses a circular cutting insert 34 for an end mill cutting tool which is held to the tool by a screw 36. When one portion of a cutting edge of the cutting insert 34 becomes worn, the screw 36 can be loosened and the cutting insert 34 can be indexed and retightened to present another portion of the cutting edge. Such an arrangement has the disadvantage, however, that it requires the tool movement to be stopped and the cutting insert to be physically unfastened, turned, and refastened each time an edge portion becomes worn. Such a procedure is very time consuming and thus decreases the cost effectiveness of the cutting insert.
Other cutting inserts have been designed which are freely rotatable relative to the cutting tool to which they are mounted. For example, U.S. Pat. No. Re. 26,637 discloses in FIG. 5 a cutter 7 which is mounted on a shaft 8 by a nut and bolt, which shaft 8 is held rotatably by a bushing 9 attached to a rotary cutting tool 1. U.S. Pat. No. 4,893,967 to Briese discloses in FIG. 11 a cutting insert 26 which has upper and lower concave surfaces and which is mounted on a spindle 168, and a split bushing 22 in which the spindle 168 is rotatably held by a thrust retainer 192, such as a nut. The split bushing 22 is held in a cutting tool 12 by a snap ring 82. As the cutting tool 12 rotates, the cutting insert 26 may rotate about its own axis.
The article entitled "Finish-Milling Plane Surface with a Rotational Tool" by E. G. Konovalov, et al. discloses in FIG. 1(b) a cutting tip 1 which rotates about its own axis as a result of interaction with a workpiece surface, and which is held on a shaft 3 by a nut. The shaft 3 rotates within an insert 4 which is pressed into a casing 8. Soviet Patent No. 387,794 to E. G. Kuzovenko, et al. discloses an independently rotating cutting tool 2 which is fixed on a support 3 and which has a flywheel 5 fastened on an end 4 of a cutting tool shaft. Although the above-noted devices allow rotation of a cutting insert, they have the disadvantage of failing to provide a means for inducing the cutting insert to rotate about its own axis as it cuts a material. Cutting inserts of the above type are thus more likely to jam or stick, or simply fail to rotate, such that the expected benefits of a rotatable insert are not achieved. Specifically, if the insert does not rotate, heat builds up in one portion of the cutting edge and that portion of the cutting edge fails relatively rapidly. Also, the cutting inserts fail to suggest the structural benefits of a rotatable cutting insert having a head and shaft which are one piece.